Just as we cannot be too sure of who will win the league is the same way that we cannot y which club will be on relegation now till the last month of the season. You should know that football is full of surprises and we should expect the unexpected as time goes by. Cagliari is facing difficulties since this season and if they don't improve, they might go to relegation, but if they improve in their performance, they will still remain in the league. As the season keep drawing close to the end, you will be surprised with the performance of some weak clubs.
But I would tend to believe that it is easier to say who might win Serie A than it is to say who will be relegated into Serie B. Inter Milan is for many reasons the biggest favorite. A draw like against Genoa can happen once in a while, this is really nothing out of the ordinary. But the kind of way how Inter Milan is winning most of their games sets them apart from the rest. Juventus Turin is result-oriented and all that counts is the win, the 3 points. Which is ok and if they are successful, they are right. But Inter Milan wants to play awesome, fun to watch football and show their opponents who the real boss is. Their goal difference is telling the whole story here. I believe that Juventus Turin is closer to losing two games in a row than Inter Milan will ever be this season.
Of course, nothing can really be completely certain at this time, because any changes will of course occur. Moreover, there will be a transfer window and ya, because there will be player transfers taking place, at least each team will get changes too. I don't know whether the changes that will occur will be changes for better performance, or maybe become the worse because anything can still happen.
But what is clear is that the teams in the lower zone will of course still be able to change but indeed, for the teams in the top position it seems like it will only be a competition between Inter and Juventus. Because ya, even though Inter and Juventus sometimes fail to get full points, at least Inter and Juventus are teams that are more consistent than other teams at this moment in the Serie A standings, of course.